126 NATURAL HISTOEY BULLETIN 



also distinguishable. Some of the plates on the papular areas 

 are enlarged and similar to those that have a central spine. The 

 madreporic plate is large, round, and covered with radial gyri. 

 It is surrounded by plates bearing larger spinules; that on the 

 adcentral side is largest. 



The adambulacral plates project into the groove; the inner 

 edge bears ten to twelve graded spines, the middle one longest; 

 the rest of the margin, on the aetinal side, bears about a dozen 

 very small conical spinelets. On the center of the aetinal face 

 there is one large, movable, conical spine. On some of the plates 

 there are one to three small spinelets around its base. (In some 

 of our specimens part of these plates have two unequal, long, 

 slender spines.) 



The interactinal plates form three series; the first has six 

 plates (three each side) ; the second has four; the third two. 

 These plates bear a set of spines about parallel with the adambu- 

 lacrals; one of the inner plates of the first row is longer and 

 larger; other small spinules cover the plates. 



Two or three pectinate pedicellariae occur on the sutures of 

 these plates, one on each series. They have five or six papillae 

 on each half. 



The jaws are prominent, each half is wedge-shaped, and bears 

 about eleven marginal spines, the two inner much the larger; 

 the lateral ones slender, subequal. Epioral spines are numerous ; 

 three inner ones are larger. 



Some of the specimens before me agree well with the charac- 

 ters given by Perrier for his original type, and agree with some 

 of his cotypes that I have studied in the Museum of Comparative 

 Zoology. Many of these are evidently immature. 



Perrier (1894, p. 271) made the presence of a group of spines 

 on the center of the disk the special character of this species 

 (under the name coronatus) and stated that this separates it 

 from all the other species of the West Indian fauna. 



In this statement he certainly went too far, for at least two 

 other species have the same feature. Very likely, therefore, he 

 still included in his species specimens of more than one species. 



He recognized two varieties : one with short and the other with 

 long rays, the latter being the typical mirdbilis, as shown above. 

 The form with short rays may be distinct. Its type was from 



